Acoustic inhibition of hydrates, scales and paraffins

ABSTRACT

Devices and methods for inhibiting the deposition of methane or natural gas hydrates, as well as scales, paraffins and other undesirable deposits within a wellbore using acoustic energy. An acoustic inhibitor is associated with a wellbore proximate the wellhead and is used to generate a low frequency acoustic energy signal that is propagated axially through the wellbore. The acoustic inhibitor preferably comprises a magneto-restrictive element that is pulsed in accordance with a predetermined frequency to generate acoustic waves in fluid that is located within the flowbore of wellbore production tubing or in a pipeline. The tubing string or pipeline is used as a waveguide to propagate the acoustic energy axially.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the use of acoustic energy to retardand prevent deposits of hydrates, scales and paraffins within a wellboreor pipeline and the components associated therewith.

2. Description of the Related Art

Multiphase flow in deep sea oil and gas wells and pipelines is anenvironment conducive to the formation of methane or natural gashydrates, which consist of gas trapped within an ice matrix. Thesehydrates can choke off or entirely plug off fluid flow through awellbore or pipeline. Typically, hydrates tend to form in specifictemperature and pressure regimes. As pressure increases, the hydrateformation temperature also increases. For pressures typically seen indeep water wells, this places the hydrate formation temperature in therange of temperatures seen at the mud line of a sea-based well (i.e.,around the ocean floor). Thus, hydrate formation generally occursproximate the ocean floor.

Removing hydrate deposits is a difficult and lengthy process. Presently,hydrate formation is often inhibited using chemicals and, in some case,heaters, for remediation of a plugged conduit. The use of inhibitionchemicals and/or heaters is logistically complex and expensive. Inaddition to hydrates, scales and paraffins also become deposited onwellbore and pipeline components during operation. These also aredetrimental to operation of valves and other components within theflowbore or pipeline.

Some arrangements are known to try to clean hydrates, scales or othermatter from wellbores using acoustic energy. However, these arrangementsgenerally rely primarily upon transmitting acoustic energy through thewalls of the flowbore or pipeline itself rather than through the fluidwithin the flowbore. The vibratory transducers used in these earlierapproaches are typically operated at high vibration frequencies, i.e.,20 kHz or higher. These high frequency vibrations are used to shatterthe matrix of an already formed hydrate plug or to remove an existingdeposit of hydrates or other matter. It is believed, however, that thesehigher frequencies are not effective in preventing the initialdeposition of hydrates and other deposits within portions of a wellboreor pipeline. Thus, these prior approaches have not been effective inpreventing the build-up of hydrates, scales or paraffins within theflowbore.

U.S. Pat. No. 4,280,557, issued to Bodine, is one example of a prioracoustic energy cleaning arrangement. Bodine describes a system forremedial cleaning of foreign matter from tubular members wherein amechanical oscillator, is secured within a wellbore casing androtationally driven to create whirling vibratory pressure action inannulus fluid. Rotation speed of the oscillator is on the order 20-100cycles per second.

U.S. Pat. No. 5,595,243, issued to Maki, Jr. et al. describes anacoustic well cleaning system wherein a sonde is lowered into awellbore. The sonde contains a number of transducers that are powered togenerate a high frequency sonic signal in the range of 20 kHz to 100kHz. Cleaning occurs as the tool is moved upwardly through a producingzone. U.S. Pat. No. 5,727,628, issued to Patzner describes a similarsystem wherein an ultrasonic cleaning unit is lowered into a wellbore bycable. The cleaning unit includes a number of magneto-restrictiveultrasonic oscillator transducers that are pulsed to produce ultrasonicwaves that are intended to clean proximate portions of the wellbore. Thetransducers are operated at a frequency in the range of 18 to 25 kHz,and preferably, at around 20 kHz.

U.S. Pat. No. 5,948,171, issued to Grothaus, teaches anelectro-hydraulic transducer device for cleaning the inner surface ofpipelines. The typical operating parameters for the device include apulse frequency of 1-25 Hz.

U.S. Pat. No. 6,405,796, issued to Meyer et al., describes an ultrasonicdevice that is suspended within a borehole by a cable and used toimprove production by breaking up particle agglomeration. The method ofuse requires that an acoustic slow wave, or the point at which themotion of solid and liquid are 180 degrees out of phase, be calculated.This calculation is a function of specific reservoir characteristics,such as reservoir permeability and aggregate porosity.

U.S. Pat. No. 6,418,960, to Mintz et al. describes a liquid deliverysystem that is configured for purging cycles between pumping cycles ofprocess fluids. Ultrasonic transducers are mounted on fluid transmissionlines and operated during the purge cycle to help remove mixed purge andprocess fluids. The preferred operating frequency range for thetransducers is from 25 kHz to 200 kHz.

U.S. Pat. No. 6,467,542, issued to Kostrov et al. illustrates a systemfor stimulation of fluid-bearing formations using resonant vibration. InKostrov's system, a wave generator is disposed into a wellbore suspendedon wireline. A vibration sensor detects the eigen frequency or bandwidthof the production formation, and the wave generator is then operated atthe eigen frequency or bandwidth.

U.S. Pat. No. 6,474,349, issued to Laker, describes an ultrasonic toolfor the cleaning of tubular members. The tool is run into a wellbore ona cable. Operation of an acoustic vibrator within the tool causescavitation that is intended to remove scales and asphaltenes in thewellbore. Laker provides no specifics with regard to the preferredfrequencies of operation for his vibrator.

U.S. Pat. No. 6,619,394, issued to Soliman et al., is directed to a wellcleaning tool that subjects substantially the same portion of a wellboreto vibratory waves produced by a plurality of vibratory wave generators.The vibratory waves may have about the same frequency or a plurality offrequencies that may overlap or be modulated across a range. This typeof system utilizes a piston pulser and a vibrating pipe to try to removealready deposited mudcake from the inside of a wellbore.

The present invention addresses the problems of the prior art.

SUMMARY OF THE INVENTION

The invention provides devices and methods for inhibiting the depositionof methane or natural gas hydrates, as well as scales, paraffins andother undesirable deposits within a wellbore using acoustic energy. In apreferred embodiment, an acoustic inhibitor is associated with awellbore proximate the wellhead and is used to generate a low frequencyacoustic energy signal that is propagated axially through the wellbore.The acoustic inhibitor preferably comprises a transducive element thatis pulsed in accordance with a predetermined frequency to generateacoustic waves in fluid located within the flowbore of wellboreproduction tubing or in a pipeline. The tubing string or pipeline isused as a waveguide to propagate the acoustic energy axially.

In preferred embodiments, the acoustic waves are generated at afrequency in a relatively low frequency range that is generally fromabout 1000 Hz to about 2200 Hz. Particularly effective frequencies forinhibiting the growth and formation of a hydrate matrix are 1130 Hz and2000 Hz. This pulsing will prevent the agglomeration of hydrateparticles that would lead to the formation of a hydrate deposit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, cross-sectional view depicting an exemplaryhydrocarbon production wellbore that includes an acoustic inhibitorarrangement constructed in accordance with the present invention.

FIG. 2 is a schematic diagram depicting the components of a currentlypreferred acoustic inhibitor, in accordance with the present invention.

FIG. 3 is a schematic operational diagram illustrating an exemplaryvibratory element used with the acoustic inhibitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an offshore hydrocarbon production well 10 thatincludes an offshore platform 12 located within the sea 14 and restingon the sea floor 16. An upper portion of the platform 12 extends abovethe surface 18 of the sea 14 and supports a production Christmas tree20, of a type known in the art for connection of suitable productionpiping and valving to a hydrocarbon production well. A riser 22 extendsdownwardly from the Christmas tree 20 and to a wellhead 24 located onthe sea floor 16. A wellbore 26 extends downwardly from the wellhead 24through the earth 28 to a hydrocarbon-bearing formation 30. The wellbore26 includes exterior casing 32 that runs along at least a portion of thelength of the wellbore 26. A string 34 of production tubing is disposedwithin the riser 22 and the casing 32. An annulus 36 is defined betweenthe production tubing string 34 and the casing 32. During production ofhydrocarbons from the production zone 30, the interior flowbore of theproduction tubing string 34 is filled with production fluid. Theinterior flowbore of the production tubing string 34 is, therefore,prone to deposits of scales, paraffins, and hydrates (hereinafter“harmful deposits”) along its length. The primary area of concern,particularly for the creation of harmful deposits is the portion of theproduction string 34 that is generally proximate mud line, or sea floor16.

In a preferred embodiment, the Christmas tree 20 and wellhead 24 includeportions of an acoustic inhibitor 40 that is associated with theflowbore 42 of the production tubing string 34, as depictedschematically in FIG. 2. The acoustic inhibitor 40 preferably includes atransducive vibratory element 44 that is formed of electro-ceramicmaterial. Applying a voltage across the element 44 causes it to expandproportionally to an expanded state (see position 44 a in FIG. 2). Whenvoltage is removed, the element 44 returns to unexpanded state. If avoltage signal is applied at a given frequency expansion and contractionoccurs in concert with the provided frequency. The vibratory element 44is actuated by an actuator that includes a signal generator 46 togenerate a sine wave electrical signal that is provided to an amplifier48 and then to the vibratory element 44 so that the vibratory element 44will be pulsed in accordance with a particular voltage and frequency.The amplifier 48 is used to boost the signal provided to the vibratoryelement 44.

The vibratory element 44 may be constructed in a number of ways. FIG. 2depicts a first embodiment wherein the element 44 is a monolithicrod-shaped member that is formed of magnetostrictive material, of aknown type. In this embodiment, a magnetic coil (not shown) used toselectively actuate the element 44 between expanded and unexpandedconditions in response to the electrical signal provided from theamplifier 48. The element 44 might also be formed as an annular memberwith a central opening that allows fluid flow through its centralopening. In addition, the element 44 might be formed of piezoelectricmaterial, of a known type, that will deform as a function of appliedvoltage from the amplifier 48.

FIG. 3 depicts one currently preferred construction for a vibratoryelement 44′. A number of circular electro-ceramic, magnetostrictive orpiezoelectric members, i.e., disks, 50 are glued or otherwise securedtogether in a stacked configuration with the electrical signal from theamplifier 48 applied to expand each of the individual members 50. Theuse of a stack of individual members 50 to form the element 44′ isadvantageous because the stacked device will require a lower voltage toachieve a maximum expansion of the members 50. The stack of circularmembers 50 is preferably encapsulated in a fluid-resistant membrane 52.The stack of circular members 50 is preferably secured to a base 54. Thebase 54 may be incorporated into or attached to the wellhead 24 and isused to position the vibratory element 44 relatively centrally withinthe flowbore 42. The function generator 46 and amplifier 48 meanwhileare preferably located at or near the Christmas tree 20 so that they maybe controlled and monitored by rig personnel.

In operation, vibration of the vibratory element 44 or 44′ generatescyclical acoustic waves, depicted at 56 in FIG. 2, within fluid in theflowbore 42. The flowbore 42 acts as a waveguide to provide axialpropagation of sonic energy. The vibratory element 44, 44′ is operatedto pulse at a frequency that is intended to inhibit growth of hydrateswithin the flowbore 42 particularly proximate the wellhead 24. Theacoustic waves 56 are generated in a relatively low frequency range thatis generally from about 1000 Hz to about 2200 Hz. Particularly effectivefrequencies for inhibiting the growth and formation of a hydrate matrixare around 1130 Hz and around 2000 Hz. In testing, these low frequencieshave been shown to be particularly effective in preventing the growth ofhydrates within a tubular member. It is believed that these lower rangefrequencies are particularly suited to preventing and retarding theinitial growth of hydrates rather than in shattering an existing matrixof already-deposited hydrates. Similarly, these frequencies areeffective in preventing initial deposits and slowing the growth ofscales and paraffin deposits within a tubular member.

The frequencies used and the configuration of the acoustic inhibitor 40is designed to optimally prevent the initial agglomeration of particlesof hydrates, scales, paraffins and other undesirable deposits ratherthan remedially cleaning deposits from a tubular member. Thus, toprovide maximum effectiveness in inhibiting deposits and growth ofhydrates, scales and paraffins, it is suggested that the signalgenerator 46 be operated to vibrate the vibratory element 44, 44′ in asubstantially continuous manner during production operations. It isnoted that use of the acoustic inhibitor 40 will not preclude theadditional use of chemical inhibitors in the flowbore 42.

Although shown here used with a sea-based well, those of skill in theart will understand that the acoustic inhibitor 40 and methods ofoperation thereof may also be used with land-based wells or withpipelines.

Those of skill in the art will recognize that numerous modifications andchanges may be made to the exemplary designs and embodiments describedherein and that the invention is limited only by the claims that followand any equivalents thereof.

1. An acoustic inhibitor for inhibiting harmful deposits within theflowbore of a tubular member containing fluids, the acoustic inhibitorcomprising: a vibratory element capable of inducing an acoustic wavewithin the flowbore; an actuator for operating the vibratory element ata frequency that inhibits deposits of hydrates within the flowbore. 2.The acoustic inhibitor of claim 1 wherein the actuator operates thevibratory element at a frequency that is from about 1000 Hz to about2200 Hz.
 3. The acoustic inhibitor of claim 2 wherein the actuatoroperates the vibratory element at a frequency that is about 1130 Hz. 4.The acoustic inhibitor of claim 2 wherein the actuator operates thevibratory element at a frequency that is about 2000 Hz.
 5. The acousticinhibitor of claim 1 wherein the actuator comprises a signal generatorthat produces a sine wave signal of particular frequency.
 6. Theacoustic inhibitor of claim 5 wherein the actuator further comprises asignal amplifier.
 7. The acoustic inhibitor of claim 1 wherein thevibratory element is formed of electro-ceramic material.
 8. The acousticinhibitor of claim 1 wherein the vibratory element is formed ofmagnetostrictive material.
 9. The acoustic inhibitor of claim 1 whereinthe vibratory element is covered with a fluid-resistant membrane. 10.The acoustic inhibitor of claim 1 wherein the vibratory elementcomprises a plurality of stacked members.
 11. A system for inhibitingdeposits and growth of harmful deposits within a tubular member, thesystem comprising: a vibratory element capable of inducing an acousticwave within the flowbore, the vibratory element comprising: a memberfashioned from a material fro the group of materials consistingessentially of electroceramic, magnetostrictive and piezoelectric; andan actuator for operating the vibratory element at a frequency thatinhibits deposits of hydrates within the flowbore.
 12. The system ofclaim 11 wherein the actuator operates the vibratory element at afrequency that is from about 1000 Hz to about 2200 Hz.
 13. The system ofclaim 11 wherein the actuator operates the vibratory element at afrequency that is about 1130 Hz.
 14. The system of claim 11 wherein theactuator operates the vibratory element at a frequency that is about2000 Hz.
 15. The system of claim 11 wherein the vibratory element iscovered with a fluid-resistant membrane.
 16. The system of claim 11wherein the vibratory element comprises a plurality of stacked members.17. A method for inhibiting deposits and growth of harmful depositswithin a tubular member comprising the step of: actuating a vibratoryelement within the flowbore of a tubular member at a frequency that isfrom about 1000 Hz to about 2200 Hz.
 18. The method of claim 17 whereinthe actuator operates the vibratory element at a frequency that is about1130 Hz.
 19. The method of claim 17 wherein the actuator operates thevibratory element at a frequency that is about 2000 Hz.